1. Field of the Invention
The present invention relates to a thermal transfer member, in which a plurality of color material layers containing specific coloring agents are disposed on one surface of a base material and which is used for a recording method through sublimation or heat migration thermal transfer, and a recording method in which the coloring agents of the thermal transfer member are thermally transferred to a transfer receiving member, e.g., photographic paper, so as to record a lightfast image.
2. Description of the Related Art
In recent years, a sublimation (or heat migration) thermal transfer system has been wide spread as a color hard copy system capable of obtaining images close to silver halide photography in, for example, a hard copy output from a digital camera. Furthermore, this thermal transfer system has a feature that color printing or photorealistic printing can be conducted on demand simply without a high equipment cost and a large space in contrast to general printing methods, e.g., offset printing and gravure printing.
In the thermal transfer system, a transfer member provided with color material layers of, for example, yellow, magenta, and cyan, which contain coloring agents, and a transfer receiving member, e.g., photographic paper, are stacked together, heat energy in accordance with the image information is applied from either side with a thermal head, a laser, or the like so as to transfer the coloring agent on the transfer member to the transfer receiving member and print an image. In this thermal transfer system, the three primary colors of yellow, magenta, and cyan are used mainly, and colors employed for a photograph are reproduced by using them alone or color mixing.
Regarding the thermal transfer system in which an image is printed by the above-described method, a keeping quality particularly important for the photograph is poor as compared with that of silver halide photography. Therefore, the keeping quality is susceptible to improvement.
As for a measure against it, some proposals related to the structure of coloring agents have been made in order to improve the lightfastness of the printed image, as disclosed in Japanese Unexamined Patent Application Publication No. 60-239289.
Individual agents exhibit excellent lightfastness and excellent heat resistance when used alone. However, in some cases, the lightfastness may deteriorate because of presence together with other coloring agents on a transfer receiving member after an image is printed, even when the coloring agent exhibits good lightfastness in monochrome. That is, regarding the lightfastness, in the case where one type of dye absorbs light on a transfer receiving member, the dye serves as a sensitizing agent (or an oxidizing agent or a reducing agent) of another coloring agent because of an interaction, and the other type of coloring agent or both coloring agents deteriorate significantly. Such a problem easily occurs, for example, in the case where a yellow coloring agent and a cyan coloring agent are present together on a transfer receiving member.
A dicyanomethine based yellow coloring agent used as a yellow coloring agent exhibits slightly poor lightfastness but exhibits excellent solubility in general-purpose solvents, e.g., methyl ethyl ketone and toluene, and a high print density can be obtained.
An indoaniline based cyan coloring agent used as a cyan coloring agent exhibits excellent lightfastness and exhibits relatively excellent heat resistance. Furthermore, a high print density can be obtained.
Regarding the thermal transfer system, in the case where color mixing is conducted by combining the above-described dicyanomethine based yellow coloring agent and the indoaniline based cyan coloring agent on a transfer receiving member, a lightfastness deterioration phenomenon due to an interaction between the yellow coloring agent and the cyan coloring agent may occur in the resulting mixed color.
Moreover, quinophthalone based yellow coloring agents described in, for example, Japanese Patent No. 3596921 and Japanese Examined Patent Application Publication No. 5-35079 exhibit excellent lightfastness, but most of them exhibit poor solubility in the general-purpose solvents and are unsuitable for responding to recent speedup and an increase in sensitivity, so that they are used merely in an auxiliary manner. The quinophthalone based yellow coloring agents exhibit relatively low level of interaction with the indoaniline based coloring agents, but interactions with coloring agents having other skeleton structures are observed.
As described above, for example, in the case where a dicyanomethine based yellow coloring agent and an indoaniline based cyan coloring agent are used, no problem occurs in, for example, the solubility in solvents. However, in the case where a yellow coloring agent and a cyan coloring agent are present together on a transfer receiving member, one of the coloring agents or both coloring agents deteriorate significantly and the lightfastness of an image is reduced.